This invention relates to a technology for establishing a logical path between communication devices.
Telecommunication carriers that use a connection-oriented communication protocol to build a transport network are known. Examples of communication protocols for building a transport network include Multiprotocol Label Switching-Transport Profile (MPLS-TP), Provider Backbone Bridges (PBB), and Asynchronous Transfer Mode (ATM). With these communication protocols, an end-to-end logical path can be built to provide a highly confidential logical path. These communication protocols also have an Operation, Administration and Maintenance (OAM) function for monitoring the logical path for the presence or absence of a failure, and an Automatic Protection Switching (APS) function for automatically switching the logical path if a failure occurs in the logical path, which means that a highly reliable logical path can be built.
On the other hand, many ISPs and corporate users (hereinafter, referred to as transport network users) use routers, which are devices for transmitting and receiving data in accordance with the IP, to build a communication network. Routers exchange routing protocols with each other, to thereby autonomously collect a connection relation between the routers in the IP layer and generate routing information. The routing information is generated by all routers that are on the same communication network, and the routers all hold the same routing information. Each of the routers transmits and receives communication data along generated logical paths.
A transport network user rents a transport network from a telecommunication carrier and uses routers owned by the transport network user to connect bases with one another. FIG. 20 is a diagram illustrating an example of a conventional transport network provided by a telecommunication carrier and connection relations that are formed to connect bases of a transport network user to one another.
A transport network 3 of the telecommunication carrier is constituted of a plurality of transport nodes 1 (1-1 to 1-n (n is 4 in the example of FIG. 20)). The transport nodes 1-1 to 1-n have interface cards (IFs) 2 (2-1 to 2-n) for connecting to routers. A logical path 7 between two of the transport nodes 1-1 to 1-n is set fixedly to these two transport nodes by a transport network logical path management server 4. Information on a logical path between two of the transport nodes 1-1 to 1-n is saved in a transport network logical path database (DB) 5, which is kept by the transport network logical path management server 4. In other words, the transport network logical path management server 4 can keep track of the state of every logical path 7 in the transport network.
The logical path 7 between two of the transport nodes 1-1 to 1-n is a logical connection and may not match the physical connection in some cases.
Bases 10 (10-1 to 10-n) of the transport network user include routers 11 (11-1 to 11-n), which connect to the transport nodes 1-1 to 1-n, and include communication terminals 12 (12-1 to 12-m). For example, the base 10-1 of the transport network user includes the router 11-1, which connects to the transport node 1-1, and includes the communication terminals 12-1 and 12-2. The communication terminals 12-1 to 12-m are, for example, routers, personal computers, or similar information devices for connecting to other communication networks.
In a mode where the routers 11-1 to 11-n and the transport nodes 1-1 to 1-n are connected in this manner, when the transport node 1-x (1≦x≦n) receives through the interface 2-x an IP packet and a routing packet that are transmitted from the router 11-x, the interface 2-x determines, based on the address for a protocol of a layer below the IP layer (for example, a Mandatory Access Control (MAC) address), which of logical paths 7 (7-1 to 7-l) in the transport network to use for the transfer of the packets. The packets for which the interface 2-x has determined a logical path are processed also in the interface 2-x into a data transfer mode of the transport network, and then are transferred to the transport node 1-y (1≦y≦n, y≠x), which is connected to the objective router 1-y. 
Japanese Patent Application Laid-open No. 2010-246138, Japanese Patent No. 3910200, and Japanese Patent Application Laid-open No. 2000-183919 can be given as the related art in which routers are connected to one another via a transport network.
FIG. 21 illustrates connection modes of the IP layer and the transport layer in which routers are connected to one another referring to Japanese Patent Application Laid-open No. 2010-246138 and Japanese Patent No. 3910200. Illustrated in FIG. 21 are connection modes of a transport layer 6 and of an IP layer 13. The communication terminals 12-1 to 12-m connected to the routers 11-1 to 11-n are omitted from FIG. 21 for simplification, as well as the transport network logical path management server 4, a transport network logical path DB 5, and the IFs 2-1 to 2-n. 
The logical paths 7-1 to 7-l of the transport layer 6 are set by the transport network logical path management server 4, and all logical path relations are saved in the transport network logical path DB 5.
The connection relations in the IP layer 13 are generated autonomously by the routers 11-1 to 11-n by exchanging routing protocols among the routers 11-1 to 11-n. Setting the logical paths 7-1 to 7-l in the transport layer 6 which constitute a full-mesh topology connecting the routers to one another puts all routers that are connected to the transport network 3 in an adjacency relation. Router-to-router logical paths 14 (14-1 to 14-l) managed by each router accordingly constitute a full-mesh topology that connects the routers 11-1 to 11-n to one another as illustrated in solid lines in FIG. 21.
Information on the logical paths 14-1 to 14-l of the IP layer 13 is held by all the routers. An increase in the number of routers connected to the transport network 3 therefore means an exponential increase in the amount of routing information held by each router. Another problem arises when, for example, a path failure occurs between the transport node 1-2 and the transport node 1-3, resulting in the loss of a path that directly connects the router 11-2 and the router 11-3, and the router 11-2 and the router 11-3 recalculate a path to set a new route. The router 11-2 and the router 11-3 transfer a routing protocol that prompts recalculation of logical paths to all the rest of routers, including ones whose communication is not affected by this failure, for example, the router 11-1 and the router 11-4, and the routers respectively execute recalculation of routing information.